Within telecommunication systems, such as within a Global System for mobile communications (GSM) Enhanced Data Rates for GSM Evolution (EDGE) Radio Access Network (GERAN) network, so called Packet Switched (PS) Temporary Block Flow (TBF) are used to enable transfer of user data between e.g. a Radio Base Station (RBS) and a Mobile Station (MS), such as a wireless device. The PS TBF is assigned a Temporary Flow Identity (TFI) value. The TFI value is uniquely identifying a TBF among concurrent TBFs in the same direction, i.e. uplink for transfer of data from the mobile station to the radio base station or downlink for transfer of data from the radio base station to the mobile station, assigned the same Packet Data Channel (PDCH) resources on the same carrier. The same TFI value may be used concurrently for other TBFs on other PDCH resources in the same direction and for TBFs in the opposite direction. Hence, a TFI is a unique identifier on a given PDCH resource. This need for TFI uniqueness within the context of any given set of PDCH resources, on a given carrier limits the number of devices that may share the same radio resources. In case of devices supporting Downlink Multi-carrier (DLMC) mode of operation, the limitation will be even more severe as each downlink TBF supported using DLMC will be assigned the use of PDCH resources on multiple downlink carriers thereby substantially increasing the number of devices being assigned the same PDCH resources for any given carrier. The DLMC mode of operation is specified in Third Generation Partnership Project (3GPP) Technical Specification (TS) 44.060, GERAN, Mobile Station (MS)-Base Station System (BSS) interface-Radio Link Control Medium Access Control (RLC/MAC) protocol.
The TFI itself is a 5-bit field encoded as binary number in the range 0 to 31, which is typically provided to the MS by the GERAN network upon TBF assignment.
A Radio Link Control (RLC)/Medium Access Control (MAC) block sent on a given uplink/downlink carrier is associated with a certain TBF. There are two types of RLC/MAC blocks; RLC/MAC data blocks and RLC/MAC control blocks for user data and control information, respectively. A RLC data block is uniquely identified by the TFI together with the direction in which the RLC data block is sent, and a RLC/MAC control block is uniquely identified by the TFI together with the direction in which the RLC/MAC control block is sent. In case Starting Sequence Number (SSN)-based Fast Ack/Nack Reporting (FANR) is used, the TFI identifying the TBF being acknowledged is included in the Piggy-backed Ack/Nack (PAN) field. Ack/Nack stands for Acknowledge/Non-acknowledge.
This means that e.g. every time an MS receives a downlink data block or control block on one of its assigned PDCHs of a given carrier, it will use the included TFI field to determine if the block belongs to any—there can be more than one—of the TBFs associated with that specific MS. If so, the block is obviously intended for the specific MS whereupon the corresponding payload is decoded and delivered to higher layers, but otherwise discarded. In the uplink direction, the behavior is the same, i.e. network uses the TFI value to identify blocks that belong to the same TBF. This is an existing mechanism used in GERAN networks for facilitating the multiplexing of multiple users on the same PDCH resources on a given carrier.
The existing TFI addressing space is considered to be insufficient assuming the current increase of PS traffic observed in GERAN networks over the world. Furthermore, the introduction of DLMC in 3GPP Release 12 makes the need to extend the TFI space acute, GP-130662 DLMC—Extended TFI Addressing Space, 3GPP GERAN#59, Ericsson & ST-Ericsson hereby incorporated by reference.
In the context of DLMC, GERAN Plenary (GP)-121158 Work Item Description (WID): Downlink Multi Carrier GERAN, 3GPP GERAN#55, Ericsson & ST-Ericsson hereby incorporated by reference, a TFI expansion is needed to increase the TFI addressing space of devices multiplexed on the same radio resources of a given downlink carrier. Solutions for TFI expansion exist for radio blocks carrying user plane payload, wherein a Cyclic Redundancy Check (CRC) code is used solely for error detection, see for example WO2013/070163, which hereby is incorporated by reference.
3GPP TS 45.003, version 11.1.0, section 6.2.1; GERAN; Channel Coding describes a bit-wise modulo two (2) addition (XOR) between a TFI and PAN CRC field. According to aforementioned WO2013/070163, this concept is extended to also apply to an extended TFI (eTFI) field and a subset of the CRC bits of a RLC/MAC data block header or a subset of the CRC bits of a PAN field. A solution in aforementioned WO2013/070163 is based on the observation that a PAN field CRC or RLC/MAC header CRC XOR'ed with an eTFI will only be decodable by a MS assigned the very same eTFI. As this prevents legacy mobiles, e.g. multiplexed on the same PDCH as a mobile having an assigned eTFI, from successfully performing a CRC check when receiving a PAN field CRC or a RLC/MAC header CRC that has been XOR'ed with an eTFI, it provides a backwards compatible extension of the TFI identifier space. This is because the impact of the eTFI XOR-ing in this case is effectively seen as an error pattern by the legacy MS, and since the CRC code cannot correct errors but only detect them, the resulting CRC check will be erroneous and the legacy MS will discard the radio block.
The solution in aforementioned WO2013/070163 is however not capable of providing the desired extension of the TFI space when addressing a FIRE-coded control block or RLC/MAC data block. Remark: “FIRE”, or “Fire”, is the name of a person contributing to the development of FIRE-codes and FIRE-coding techniques. The desired extension cannot be provided because the FIRE-code is a class of cyclic block codes used both for burst error correction and error detection. The burst error correction capability of the FIRE-code is defined by a length “b” of the shortest uncorrectable burst error, Digital Communications (5th edition), Proakis & Salehi, McGraw-Hill International, ISBN-13: 978-0072957167.
As is known in the art, a FIRE-code is a cyclic burst error correcting code over GF(q) with the generator polynomial g(x)=(x2t-1−1)p(x)
where p(x) is a prime polynomial with degree m not smaller than t and p(x) does not divide x2t-1−1. Block length of the fire code is the smallest integer n such that g(x) divides xn−1. Here the FIRE code is defined over a finite field GF(q) of block length n. See also http://en.wikipedia.org/wiki/Cyclic_code and more detailed in “Code Design for Dependable Systems: Theory and Practical Applications”, July 2006, by Eiji Fujiwara, printed by Wiley, ISBN: 978-0-471-75618-7.
This implies that if the solutions proposed in aforementioned WO2013/070163 would be applied on a FIRE-coded radio block, a legacy MS would treat the XOR'ed eTFI bits as an error sequence, correct them and then consider the radio block as valid at which point it could erroneously act on it, e.g. if the legacy TFI provided in the radio block header of a FIRE-coded control block addressed to a MS operating in DLMC mode happens to match the TFI assigned to a legacy MS. Hence, a problem may be that the intended segregation between legacy and new eTFI aware MSs is broken and an extension of the TFI field is no longer feasible.